1. Field of the Invention
The present invention relates to a method of judging a residual film by an optical measurement, particularly, to a method of judging a residual film by means of a spectral reflection interferometer in the inspecting step involved in the manufacturing process of a semiconductor device.
2. Description of the Related Art
In the conventional method of measuring a film thickness by using a spectral reflection interferometer, fitting is performed between the measured reflectance spectrum and the reflection spectrum calculated from an expected model of a stacked film so as to determine the film thickness, thereby judging the laminate structure of a sample. In the conventional method, however, the fitting becomes poor if the structure of the film to be measured differs from that of the optical model used for the film thickness calculation, with the result that it is possible for the judgment to be erroneous.
In CMP of a Cu film, which is carried out for forming a Cu damascene wiring over a Cu buried wiring with an interlayer insulating film interposed therebetween, a Cu film and a barrier metal (BM) film are polished so as to remove completely the Cu film and the barrier metal (BM) film in a field portion other than the wiring section while allowing the Cu film and the barrier metal (BM) film to be left unremoved in the wiring section alone. Therefore, under the state that the Cu film is left unremoved, the residual film in the field portion has a stacked structure of a Cu film/BM film/interlayer insulating film/Cu buried wiring. It follows that it is necessary to carry out the film thickness calculation while changing the thickness of each of at least the Cu film, the BM film and the interlayer insulating film, leading to the requirement of a tremendous calculation amount.
Such being the situation, it is conceivable to decrease the calculation amount by dividing the situation into several cases as follows depending on the CMP treatment.
Specifically, the state of the field portion can be classified into at least the three states given below:
a) Presence of a Cu residual film (NG—additional polishing);
b) Presence of a BM residual film (NG—additional polishing);
c) No residual film (finish OK)
It is conceivable to classify the state of the field portion into the three states given above and to carry out the film thickness calculation while changing the thickness of each of the uppermost layer and the layer immediately below the uppermost layer. In this method, however, it is necessary to carry out the film thickness calculation by assuming the construction of each of the layers, and it is difficult to classify the state into suitable cases. Under the circumstances, a simpler method is required for judging the residual film in the field portion.